Oscar-winning actress Shirley MacLaine joins the cast of the period drama as Cora's mother Martha, who makes a grand entrance when she arrives at Downton for Matthew and Mary's wedding. However, with the couple struggling to stay united as their big day looms, will Martha's Atlantic crossing have been for nothing? Meanwhile, Mr Carson runs the rule over new footman Alfred, and Robert receives news that could leave him facing the greatest crisis of his life - and plunge the rest of the household into chaos.